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Skriven 2005-01-14 16:40:10 av TLewis (1:261/38)
Ärende: Re: [C] Passing an enumerated data value
================================================
From: TLewis@mcleodhealth.org

Thanks Jonathan.  Based on your program,  I went back to my original and moved
the ENUM statement above the prototype, and it compiled with no problem.  I
should have thought about that.  It makes sense that a prototype cannot use an
enum data type before the enum data type is defined.

Tim




Jonathan Guthrie <jguthrie@brokersys.com> Sent by: c-bounces@snippets.org
01/14/2005 03:34 PM
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Re: [C] Passing an enumerated data value






On Fri, 2005-01-14 at 13:46, TLewis@mcleodhealth.org wrote:
> I want to pass an enumerated data type to a function.  I have code below
> that works, but I want to know if it is "proper" coding.  I tried using
> "ENUM" in my function arguments, but that does not work.
>
> Thanks,
> Tim
>
> #include <stdio.h>
> void ShowPosition(int);
>
> enum POSITION{TOP,BOTTOM};
>
> main() {
> printf("\nMain routine");
>
> ShowPosition(TOP);
>
> }
>
> void ShowPosition(int POSITION) {
>
> if (POSITION == TOP)
>     printf("\nPostion is top");
> if (POSITION == BOTTOM)
>     printf("\nPosition is bottom");
> }

I don't know what you mean when you say that you "tried using 'ENUM' in my
function arguments, but that does not work."  I turned your program into this
program:
#include <stdio.h>

enum POSITION{TOP,BOTTOM};
void ShowPosition(enum POSITION);

main() {
printf("\nMain routine");

ShowPosition(TOP);

return 0;
}

void ShowPosition(enum POSITION POSITION) { if (POSITION == TOP)
printf("\nPostion is top");
if (POSITION == BOTTOM)
printf("\nPosition is bottom");
}


This program compiles and runs correctly when I use gcc V3.3.5 on my main
development computer.

The changes I have made are these:  Move the declaration of ShowPosition until
after the definition of the "enum POSITION" type.  Update the type of the
declared argument to ShowPosition from int to "enum POSITION". Add a return
value from main, because main is declared to return an int value.  Update the
declaration of the POSITION argument to ShowPosition's definition to be "enum
POSITION" rather than int.  Note that "enum POSITION" is the type.  Although
this works (because variable names are in a different name space from the name
space that holds the names of enums) it would be better for the name of the
argument in ShowPosition to be called something else, like p.

Note that many people (including myself) like using typedefs and doing
something like

"typedef enum POSITION{TOP, BOTTOM} position_t;", and then using type type
"position_t" everywhere where "enun POSITION" goes in the program I modified
above.  The "_t" suffix in this case means that it's a type, so I would read
that aloud as "position type".  I can re-write your code in that style, if
you'd like, but I'd also want to do things like move the definition of
ShowPosition to before main so that I don't have to explicitly declare it and
whatnot.  You also might want to consider specifying values for top and bottom
(and, I presume, left and right) so that they can be used as bitmasks, but that
presupposes some things about your application.


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